As a lighting device for lighting the interior of a room or a lighting device used for a backlight of a liquid crystal display device, one known lighting device is a lighting device including LEDs arranged two-dimensionally.
Patent Literature 1 discloses a lighting device, mounted on a wall surface such as a ceiling, for lighting the interior of a room. Such a lighting device includes LEDs arranged concentrically on a circular mounting substrate. As the lighting device for lighting the interior of a room, lighting devices of various planar surface shapes are used such as a circular lighting device, like the lighting device disclosed in Patent Literature 1, and a quadrangular lighting device.
A liquid crystal display device is often designed such that an image display region is quadrangular in shape. Accordingly, a light-emitting region of a backlight for lighting a liquid crystal panel is generally quadrangular in shape, too.
Further, a liquid crystal display device using a direct-type backlight, such as mainly a television, employs the so-called local dimming technique of achieving high contrast and low power consumption by performing luminance control individually on a plurality of divisional regions into which a display region is divided.
(a) of FIG. 11 is a plan view illustrating the configuration of a direct-type rectangular backlight, and (b) of FIG. 11 is a cross-sectional view of the backlight illustrated in (a) of FIG. 11.
The backlight 101 illustrated in FIG. 11 is a backlight employing the local dimming technique. In the backlight 101, LEDs 111 are arranged in rows and columns in a matrix manner on the mounting substrate 110. A surface of the mounting substrate 110 is coated with a material with high reflectivity so as to reflect light beams from the LEDs 111. A diffuser 113 is disposed such that the LEDs 111 are covered with the diffuser 113. The diffuser 113 and the mounting substrate 110 are surrounded at their edges by a frame 112.
The backlight 101 has a light-emitting region rectangular in shape. As indicated by broken lines in (a) of FIG. 11, the areas of divisional regions 101R into which the light-emitting region is divided in a grid pattern are equal.
Thus, allowing the LEDs 111 to emit light beams uniformly makes the divisional regions 101R uniform in luminance. This makes it easy to perform luminance control individually on the divisional regions 101R. Thus, the local dimming technique can be employed with reduced variations in luminance between the divisional regions 101R.